Coils of this type are sufficiently known. In the case of these known coils, the individual windings, the start winding, the main winding and the end winding are wound onto a coil body separately from each other and the respective end portions of the individual windings are soldered or welded together. This mode of operation is very complex from a manufacturing point of view and, because of the soldering joints or welding joints, the entire coil arrangement contains potential sources of faults since, in this region, transition resistances or, in the course of the lifespan of such a coil arrangement, also interruptions in the current flow can occur, for example due to soldering joints which break because of mechanical vibrations. In addition, the windings must be placed in part above the soldering or welding joints.
It is the object of the present invention to configure a generic coil such that the production process is simplified and the susceptibility to defects in the finished product is reduced. In addition, the coil is intended to be able to be contacted as simply as possible. This has been difficult to date in particular if wires with a diameter of 50 μm or less are used since thin wires of this type can be contacted only with difficulty using conventional methods because of the lack of rigidity therein. Both the production of the coils and the contacting thereof are intended furthermore to be able to be achieved, even in large-scale production, simply, rapidly and above all without defects.
This object is achieved by the features indicated in the independent claims.
By providing a single winding wire for the main winding, the start winding and the end winding, no connection points occur between the respective windings, as a result of which both the manufacturing process is simplified and accelerated and the susceptibility to defects is reduced and hence the lifespan of the coil arrangement is increased.
Advantageous developments of the electric coil according to the invention are indicated in the sub-claims.
Preferably, at least the main winding, preferably also the start winding, is wound directly onto the coil core. In this embodiment, an additional coil body can be dispensed with so that the costs for production of a coil are reduced and also the constructional size of the coil in the radial direction is reduced. The coil body can in principle have any cross-section, there are possible in particular a rectangular or also a circular cross-section.
The coil core has thereby preferably been machined (barrel machined) with the help of a grinding process so that its surface is free of burrs and uneven regions.
Furthermore, it is advantageous if the coil core is provided at least in the region of the main winding with an insulating layer which is applied preferably on the coil core and if at least the main winding, preferably also the start winding, is wound onto the insulating layer. Provision of this insulating layer increases the reliability of the coil arrangement in that the risk of the insulation surrounding the winding wire rubbing on the coil core is reduced. The insulating layer applied directly on the coil core thereby assumes, in contrast to an additional coil body provided in the state of the art, a merely insignificant additional radial constructional space. The insulating layer can comprise suitable insulating tape which is wound around the coil body. However, in particular if the coils are manufactured on fairly large scales, this preferably concerns a polymer layer which is applied on the coil core with the help of a suitable coating method. A p-xylyene coating for example is particularly well suited, said coating having been produced by a chemical gas phase deposition. This type of coating is distinguished inter alia by its good electrical insulating properties even with very thin layers.
According to one embodiment of the invention, the end winding surrounds a portion of the main winding. The position of the end winding on the main winding can thereby be chosen without restriction so that any position of the end winding which is determined merely by the requirements of the intended application of the coil can be chosen. In addition, this arrangement makes possible a comparatively compact design.
According to an alternative embodiment, both the end- and the start winding is situated on the outside of the central main winding. This arrangement leads to an altogether flatter coil, which can be advantageous according to the constructional space present.
A further particularly advantageous embodiment of the invention is distinguished in that the respective number of turns of the coil wire of the start winding and of the end winding is calculated such that the respective electrical efficiency of the start winding and of the end winding is within prescribed tolerances after completion of the contacting with respective electrical supply lines. In this way, the electrical efficiency of the entire coil can be established precisely during manufacture and be retained within a prescribed tolerance range so that the manufacturing quality is substantially improved relative to conventional manufacturing methods.
The coil wire is coated, as normal, with a varnish, and in fact preferably with a so-called baked varnish, i.e. with an adhesive varnish, the adhesive effect of which is activated by heat. The present invention is suitable in particular for very small coils in which very thin wire is used, for example wire with a diameter in the range of less than 50 μm.
In the case of one method according to the invention for contacting a coil, in particular a coil according to the invention, a first contact of an electrical supply line, which is to be connected to the start winding, is connected to at least one external turn of the start winding in an electrically conductive manner, and a second contact of an electrical supply line, which is to be connected to the end winding, is connected to at least one external turn of the end winding in an electrically conductive manner.
The connection between the contacts of the electrical supply line and of the start- or the end winding is thereby produced according to the invention by welding or soldering, respectively a plurality of turns of the start- or of the end winding being able to be connected to the respective contacts of the electrical supply line in an electrically conductive manner. Preferably, a respectively suitable laser is thereby used for welding or soldering.
According to a particularly advantageous embodiment of the invention, the contacts of the electrical supply line have respectively one recess in an attachment region, firstly the attachment region being placed, during production of the connection, on the winding to be contacted such that this recess contacts the winding, and subsequently a laser beam being directed towards the attachment region in the region of the recess. This recess is preferably groove-shaped, a V- or U-shaped cross-section having proved to be particularly advantageous. The attachment region of the contact can be formed from a simple metal sheet, for example a copper sheet, which is provided with the V-shaped or a U-shaped profile in order to form the preferably groove-shaped recess. In this case, the connection can then be a welded connection since the copper sheet is connected directly to one or more coil wires. In order to achieve the required high temperature (here the melting temperature of copper), a laser with a correspondingly high energy density must be used.
Alternatively, the attachment region can be coated with a solder in the region of its recess also on the outside thereof, i.e. on the side which points in the direction of the coil, so that a soldered connection is produced with the help of the laser. Both a hard solder, such as for example the silver-phosphorus mixture which is marketed under the trade name Silfos, and a soft solder, such as for example tin, can thereby be used. In order to produce corresponding temperatures, lasers with a lower energy density suffice.
During the welding or soldering process, the metal sheet coated possibly with a solder is heated so that the varnish or baked varnish layer, with which the wires are coated, becomes plastic. The metal sheet drops with the preferably groove-shaped recess firstly between the turns of the winding to be contacted and displaces the plasticised baked varnish. A welded or soldered connection is produced between the attachment region of the contact, provided with a groove, and the wires of the uppermost turns of the winding to be contacted, via which the desired electrical connection is produced.
The quality of the welded or soldered connection between the wires of the coil and the contacts is determined primarily by the coupling of the laser beam into the material. In the case of non-uniform surface structures, a non-uniform and barely predictable coupling is obtained. As a result of the recess configured in the attachment region, a significant improvement is achieved here. The laser beam directed into the recess is reflected on the lateral walls thereof so that the energy is distributed uniformly in a precisely defined region. Particularly good contacting is thereby achieved with a groove-shaped recess. This can basically have any cross-section. A substantially V-shaped profile has proved to be particularly advantageous, a U-shaped cross-section is likewise conceivable.
According to a particularly preferred embodiment of the invention, the number of turns connected to the respective contact in an electrically conductive manner is chosen such that the electrical properties of the entire coil are within prescribed tolerances. For this purpose, an electrical variable, such as the resistance, of the coil can be measured, for example during the welding or soldering. When the desired value is reached, the laser beam is interrupted so that the joining process is interrupted. In this way, the coil can be manufactured such that the start winding and the end winding are negligible with respect to the overall electrical properties of the coil. The electrical properties of the coil are hence determined virtually exclusively by the main winding.